1. Field of the Invention
This invention relates to devices for controlling the of coolant to internal combustion engines. More particularly, the invention relates to an improvement in the variable control of coolant flow in response to engine temperature changes by means of a thermostat.
2. Description of Background Art
Most motor vehicles use internal combustion engines which are cooled by a closed cycle liquid coolant system. Nearly all such engines employ a temperature sensitive thermostatic valve, commonly referred to as a thermostat, to control the rate of flow of coolant through internal passageways or water cooling jackets within the engine block.
In a typical engine coolant system, liquid coolant absorbs engine heat by passing through internal engine passageways in thermal contact with the combustion chambers of the engine. The heated coolant is pumped from an outlet tube into an air-to-liquid heat exchanger referred to as a radiator. Air drawn through the radiator by means of a rotary fan and/or motion of the vehicle lowers the temperature of the coolant. This coolant then exits the radiator at a lower temperature, and is recirculated to an inlet tube to the engine water jacket system, completing a circuit for the closed loop cooling system.
The operating efficiency and smoothness of typical internal combustion engines is usually relatively poor until the temperature of the engine block has reached a certain minimum value. For typical engines, the coolant temperature at which reasonable engine operating efficiency is to 180.degree. F.
The overall heat transfer capability of the engine's cooling system must be great enough to keep the engine from reaching destructively high temperatures, even when operated under high speed, high load conditions at hot desert temperatures. If this full heat transfer capacity were employed immediately after a cold engine has been started, it would take an excessively long period for the engine to warm up to the proper operating temperature. This is especially true when the engine is started in cold weather.
To enable more rapid warm up of an engine to a proper operating temperature, means were long ago devised and incorporated into engines to inhibit the heat transfer capability of the engine's cooling system during warm up. The most commonly used means for inhibiting initial heat transfer capability and thereby speeding engine warm up is a thermostatic valve or thermostat. The thermostat is usually placed in the engine's PG,4 coolant outlet tube, directly in contact with the coolant. When the engine is first started cold, the thermostat is in a fully closed position. In this position, no coolant is permitted to flow, in spite of the hydrostatic pressure exerted on the thermostat by the engine's water pump. Thus, the cooling capacity of the system is greatly diminished, permitting the engine and coolant to warm up rapidly.
Thermostats are so constructed that when the temperature of coolant reaches a pre-determined value, a temperature responsive, bimetallic element, evaporating liquid or wax pellet within the thermostat opens a valve, allowing coolant to flow through the thermostat. This opening temperature is usually selected to be 160.degree. F., 180.degree. F., or 212.degree. F.
The failure rate of typical thermostats used in motor vehicle engines is relatively high.
If the thermostat fails in a closed position, engine overheating can occur, especially in warm weather. If the thermostat fails in an open position, the engine can take an excessively long period to reach operating temperatures. In very cold weather, a thermostat which has failed in an open position can prevent the engine from ever reaching a proper operating temperature. Under these circumstances, the coolant temperature will also be too low to properly operate the heater within the driver/passenger compartment, resulting in uncomfortably or dangerously low temperatures there.
Because of the problems caused by a failed thermostat, it is necessary or at least desirable to promptly replace the faulty thermostat. When this must be done in a remote location by the motorist, the replacement process can be troublesome, for the following reasons.
In a typical installation of a thermostat on a motor vehicle engine, the thermostat is positioned within a recess on a cast metal fitting on the upper post of the engine block, and retained therein by a thermostat housing in the form of a mating cast metal tube having a flange bolted to the engine block. A rubber hose clamped around the thermostat tubing connects to the radiator.
Replacing a thermostat conventionally mounted as described above requires use of a wrench to loosen and retighten the bolts, a new thermostat and gasket, and gasket cement to assure a watertight seal is made when bolting the thermostat housing to the engine block.
Even if the owner possesses the proper tools and materials to replace a thermostat, problems can arise when attempting to replace the thermostat. Because the bolt threads and engine block threads are subject to frequent heating and cooling cycles and contact with corrosion-accelerating coolant, the bolt threads frequently become "frozen" to the engine threads, causing a bolt to break off when a large torque is applied to the bolt in an attempt to loosen it. Also, the flat mating planes of the engine block and thermostat housing flange must be carefully scraped clean of adhering pieces of gasket and gasket cement, to ensure an effective seal. This must be done while taking care not to gouge either mating surface.
After installing a new thermostat, care must be taken to seat the thermostat properly in the engine block recess, to properly install the gasket and gasket cement and properly seat the thermostat housing flange with respect to the thermostat and engine block. Finally, the fastening bolts must be installed with sufficient torque so as to insure a liquid-tight seal, but not so tight as to risk shearing off the bolt head.
With the problems with removal and replacement of conventionally mounted thermostats in mind, the present invention was conceived of.
Bolesky, in U.S. Pat. No. 2,479,034, Oct. 12, 1945 discloses a thermostatic valve for insertion in-line between two flexible hoses. The valve has a cylindrical valve chamber made in two telescoping parts of thin-walled metal. A thermostatic valve member in the shape of a helix is contained within the valve chamber.
Friesmuth in U.S. Pat. No. 2,996,254, Aug. 15, 1961 discloses a pellet-type thermostat having an enlarged circular flange clampingly engaged in an annular recess formed between a lower housing and upper housing.
None of the prior art developments in the field of automotive thermostats addresses the specific problem of providing a thermostat which simplifies the replacement of worn-out thermostats.